Resist composition with radiation sensitive acid generator

ABSTRACT

The invention relates to a polymeric, radiation-sensitive resist composition comprising (i) iodonium sulfonate radiation sensitive acid generator; (ii) a polymer; and (iii) an acid labile compound.

FIELD OF THE INVENTION

The present invention relates to an improved resist composition havingan ionic, radiation-sensitive acid generator.

BACKGROUND OF THE INVENTION

There is a desire in the industry for higher circuit density inmicroelectronic devices which are made using lithographic techniques.One method of increasing the number of components per chip is todecrease the minimum feature size on the chip. The use of shorterwavelength radiation (e.g. deep UV e.g. 190 to 315 nm) than currentlyemployed mid-UV spectral range (e.g. 350 nm to 450 nm) offers thepotential for higher resolution. However, with deep UV radiation, fewerphotons are transferred for the same energy dose and higher exposuredoses are required to achieve the same desired photochemical response.Further, current lithographic tools have greatly attenuated output inthe deep UV spectral region.

In order to improve sensitivity, several acid catalyzed chemicallyamplified resist compositions have been developed such as thosedisclosed in Ito et al. U.S. Pat. No. 4,491,628 (Jan. 1, 1985) andNalamasu et al., "An Overview of Resist Processing for Deep-UVLithography", J. Photopolym Sci. Technol. 4, 299 (1991). The resistcompositions generally comprise a photosensitive acid generator such astriphenylsulfonium triflate and an acid sensitive polymer. The polymerhas acid sensitive side chain (pendant) groups which are bonded to thepolymer backbone and are reactive towards a proton. Upon imagewiseexposure to radiation, the photoacid generator produces a proton. Theresist film is heated and, the proton causes catalytic cleavage of thependant group from the polymer backbone. The proton is not consumed inthe cleavage reaction and catalyzes additional cleavage reactionsthereby chemically amplifying the photochemical response of the resistto increase the quantum yield value above 1. The exposed polymer issoluble in polar developers such as alcohol and aqueous base while theunexposed polymer is soluble in nonpolar organic solvents such asanisole. Thus the resist can produce positive or negative images of themask depending on the selection of the developer solvent.

Although these resist compositions generally have suitable lithographicsensitivity, their performance can be impaired in the presence ofairborne basic chemical contaminants which are present in amanufacturing site. Recently, there has been developed a photosensitiveresist which exhibits surprising stability in the presence of airbornechemical contaminants. The resist comprises a photosensitive acidgenerator and (ii) a polymer comprising hydroxystyrene and acrylate,methacrylate or a mixture of acrylate and methacrylate. The resist hashigh lithographic sensitivity and high thermal stability. However, thereis a continuing desire in the industry to enhance the performance ofresist compositions such as image resolution and process latitude.

It is therefore an object of the present invention to provide animproved chemically amplified resist composition for use insemiconductor manufacturing.

Other objects and advantages will become apparent from the followingdisclosure.

SUMMARY OF THE INVENTION

The present invention relates to a polymeric, radiation-sensitive resistcomposition comprising (i) iodonium sulfonate radiation sensitive acidgenerator; (ii) a polymer; and (iii) an acid labile compound.

The acid labile compound is preferably chemically bonded to the polymer.Upon exposure to acid, the acid labile compound undergoes a polaritychange which results in dissolution differentiation. The acid labilecompound is preferably a compound having an acid cleavable ester group.The resist has good solubility and adhesion, high lithographicsensitivity, high contrast and is solvent developable. The photoresistcomposition of the present invention is useful in semiconductormanufacturing to make integrated circuit chips. The present inventionalso relates to the process for making a resist image on a substrateusing the resist composition of the present invention.

A more thorough disclosure of the present invention is presented in thedetailed description which follows.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an acid catalyzed, chemicallyamplified, polymeric radiation-sensitive resist composition comprising(i) ionic iodonium sulfonate radiation sensitive acid generator; (ii) apolymer; and (iii) an acid labile compound.

The key feature of the present invention is the ionic iodonium sulfonateradiation sensitive acid generator. A preferred class of generator isthe diaryl iodonium (alkyl or aryl) sulfonate having the formula.

    RR'I.sup.+ R"SO.sub.2 O.sup.-

wherein R and R' are aryl such as phenyl optionally substituted withlower C₁₋₆ alkyl substituents and R" is C₁₋₁₀ alkyl, haloalkyl or cyclicalkyl or aryl such as phenyl optionally substituted with lower C₁₋₆alkyl substituents. Preferred iodonium cations are bis(p-t-butylphenyl)iodonium, bis(p-tolyl) iodonium and bis(phenyl) iodonium. Preferredsulfonate anions are camphorsulfonate, p-methylbenzene sulfonate (tosylanion) and trifiuoromethane sulfonate.

The iodonium sulfonates of the present invention have high thermalstability e.g. thermally stable to a temperature >150° and also formacids upon exposure to radiation which have low volatility. The iodoniumcamphorsulfonate forms a weak acid upon exposure to radiation which isuseful in certain applications.

The second component of the resist composition is a compound having anacid labile group.

Preferred acid labile groups are acid cleavable groups. The preferredacid cleavable groups are ester groups such as t-butyl andα-methylbenzyl esters of carboxylic acids and t-butylcarbonates ofphenols. Other suitable acid labile groups include tetrahydropyranyl orfuranyl ethers, trimethylsilyl or t-butyl(dimethyl)silyl ethers, andt-butoxycarbonylmethyl ether of phenol. However, it is understood that awide range of acid labile groups are operative in the process of thepresent invention such as those disclosed in Ito et al. U.S. Pat. No.4,491,628, the disclosure of which is incorporated herein by reference.Brunsvold et al., U.S. Pat. Nos. 4,931,379 (Jun. 5, 1990) and U.S. Pat.No. 4,939,070 (Jul. 3, 1990) disclose suitable thermally stable acidlabile groups and associated polymer resists and the disclosure ofBrunsvold is also incorporated herein by reference. The presence ofacidic groups such as phenols or carboxylic acid groups in the filmtends to thermally destabilize the acid labile group toward thermalcleavage. Certain acid labile groups may be unsuitable in the presenceof phenolic or carboxylic acid groups due to their thermal and/orhydrolytic instability.

Preferably the acid labile compound is chemically bonded to the polymer.Suitable polymers are vinyl polymers.

The vinyl polymer is a polymer derived from vinyl monomer. The vinylpolymer can be a homopolymer, a copolymer or terpolymer. The vinylpolymer will generally have a number average molecular weight of about5000 to about 50,000 and preferably be transparent in the U.V. suitablyat least 30% transmission/micrometer at 248 nm and more preferably atleast 50% transmission/micrometer at 248 nm and more preferably at least65% transmission/micrometer. Suitable base soluble vinyl polymers arepoly(hydroxystyrene), poly(vinylbenzoic acid), poly(acrylic add),poly(methacrylic acid), polymaleimide and copolymers thereof. Thepreferred polymers are (i) a copolymer comprising the reaction productof hydroxystyrene and acrylate or methacrylate and (ii) a copolymercomprising the reaction product of (i) acrylic acid, methacrylic acid,or mixtures thereof; and (ii) methacrylate, acrylate, or mixturesthereof.

In the preferred embodiment of the present invention, the polymercomprises acid labile groups pendant from the vinyl polymer backbone.The acid labile groups inhibit the dissolution of the polymer inalkaline developer or polar solvent. After imagewise exposure andheating, the photogenerated acid converts the acid labile group fromdissolution-inhibiting to base-soluble functionality, thereby enablingimage development of the film.

The process of the present invention for making a resist image on asubstrate comprises three steps. The first step of the process involvescoating the substrate with a polymeric film comprising (i) a radiationsensitive acid generator (ii) a polymer and (iii) an acid labilecompound, all dissolved in a suitable solvent. Suitable substrates arecomprised of silicon, ceramics, polymer or the like. Suitable organiccasting solvents include diglyme, methyl cellosolve acetate,cyclohexanone, propylene glycol methyl ether acetate, ethyl lactate andthe like. The film will preferably comprise about 80 to about 99.5weight % of the polymer having pendant acid cleavable substituents (e.g.ester substituents) and about 20 to about 0.5 weight % of the acidgenerator both dissolved in the organic solvent.

Optionally, the film can contain additives such as polymers and smallmolecules to adjust the films dissolution rate, etch resistance, opticaldensity, radiation sensitivity, adhesion and the like. The film can becoated on the substrate using art known techniques such as spin or spraycoating, doctor blading or electrodeposition. After the film is coatedon the substrate, it is generally heated to remove the solvent from thefilm.

In the second step of the process, the film is imagewise exposed to alow dose of radiation suitably electromagnetic or electron beamradiation preferably electromagnetic, preferably deep ultraviolet orx-ray more preferably deep ultraviolet radiation at a wavelength ofabout 190 to 315 nm more preferably at a wavelength of about 250 nm.Suitable radiation sources include mercury, mercury/xenon, and xenonlamps, excimer laser, electron beam or x-ray. Upon exposure acid isgenerated.

After the exposure, the film is preferably heated again to an elevatedtemperature. After exposure and heating, the side chain acid cleavableester groups pendant from the polymer backbone are cleaved e.g. via achemically amplified process, to form polar recurring units on thepolymer backbone which are soluble in alkaline developer or polarsolvents. The post-exposure heating enhances the cleavage of the estergroups. The cleavage of the ester groups alters the dissolution rate ofthe polymer and the resulting differential solubility between theexposed and unexposed areas of the film enables development of the imagein the film.

The last step of the process of the present invention involvesdevelopment of image in the film. Suitable development techniques areknown to those skilled in the art. The image can be solvent developedpreferably in an aqueous base solvent without metal ions such as aqueoustetraalkyl ammonium hydroxide to produce a positive tone image. Theimage in the film has high resolution and straight side walls.

After the substrate has been exposed by development, circuit patternscan be formed in the exposed areas by coating the substrate with aconductive material such as conductive metals by art known techniquessuch as evaporation, sputtering, chemical vapor deposition or laserinduced deposition. Dielectric materials may also be deposited bysimilar means during the process of making circuits. Inorganic ions suchas boron, phosphorous or arsenic can be implanted in the substrate inthe process for making p or n doped circuit transistors. Other means forforming circuits will be known by those skilled in the art.

The following examples are detailed descriptions of methods ofpreparation and use of the process of the present invention. Thedetailed preparations fall within the scope of, and serve to exemplify,the more generally described methods set forth above. The examples arepresented for illustrative purposes only, and are not intended as arestriction on the scope of the invention.

EXAMPLE 1 Preparation of Bis-(p-t-Butyphenyl)iodoium Camphorsulfonate

To a 500 mL 4-necked Morton flask equipped with a mechanical stirrer,125 mL addition funnel, thermocouple and argon inlet, was added 42.2 g(0.33 mol) of t-butylbenzene and 66 mL of acetic anhydride. The solutionwas stirred and 33 g (0.15 mol) of potassium iodate was added. Theresulting suspension was cooled to 0° C. under argon. Meanwhile, to a250 mL 3-necked round bottom flask equipped with an overhead stirrer, Arinlet, thermocouple, and addition funnel was added 66 mL of aceticanhydride and the solution cooled in ice to 0° C. The addition funnelwas charged with 21 mL of conc. H₂ SO₄ which was then slowly dropwiseover 1 hour maintaining a temperature <15° C. The resulting viscoussolution was then transferred to the addition funnel on the Morton flaskand added dropwise with vigorous stirring over 2 hours maintaining atemperature below 10° C. The orange suspension was then allowed toslowly warm to 22° C. overnight. The mixture was recooled to 0° C. andthe addition funnel charged with 65 mL of water. The water was addedvery slowly at first, maintaining a temperature below 10° C. As theaddition proceeded, it became possible to increase the flow rate andstill maintain a temperature below 10° C. Once the addition wascomplete, 50 mL of ether was added in one portion and the mixturefiltered through Celite. The water remaining in the filter bed waschased through with 50 mL of hexane. The filtrate was then washed with6×150 mL of hexane. Meanwhile, to a 1000 mL 4-necked round bottom flaskequipped with an overhead stirrer, a thermowell and a 500-mL additionfunnel, was added 200 mL of water and 55.3 g (0.238 mol) of10-camphorsulfonic acid. The flask was cooled in ice and the solutionneutralized with 10.4 mL of conc. NH₄ OH (14.8M). The addition funnelwas then charged with the hexane-washed aqueous filtrate which was addeddropwise over I hour with vigorous stirring. The white precipitate wasfiltered and air-dried overnight on the filter. The crude product wasrecrystallized from ethyl acetate/IPA to yield 54.8 g (58%) of the titlecompound as white flakes, mp 218°-220° C.(w/decomp.).

EXAMPLE 2 Resist Composition

A copolymer of t-butyl acrylate with p-hydroxystyrene (20 g) wasdissolved in 100 g of propylene glycol methyl ether acetate, to whichwas added di(p-t-butylphenyl)iodonium camphorsulfonate at aconcentration of 2.5% to the total solid. The solution was filtered(0.2μm).

EXAMPLE 3 Lithographic Results

The above resist composition was spin-coated onto 6" silicon wafersprimed with hexamethyldisilazane. The resist film thus formed was bakedat 150° C. for 60 sec. and exposed to a varying dose of 248 mn deep UVradiation on a Micrascan II. The exposed resist film was postbaked at150° C. for 90 sec. and developed with a 0.26N tetramethylammoniumhydroxide aqueous solution for 60 sec., followed by rinsing with water.Linear resolution to 225 nm was obtained at 6.25 mJ/cm² and the depth offocus for 250 nm line/space patterns was 1.2 μm.

Although this invention has been described with respect to specificembodiments, the details thereof are not to be construed as limitationsfor it will be apparent that various embodiments, changes, andmodifications may be resorted to without departing from the spirit andscope thereof, and it is understood that such equivalent embodiments areintended to be included within the scope of this invention.

We claim:
 1. A radiation sensitive resist composition comprising (i) bis(lower alkyl phenyl) iodonium camphorsulfonate and (ii) a copolymercomprising hydroxystyrene and acrylate or methacrylate having an acidclearable substituent.